When applying a coating material, for example, a cementitious mortar, to an interior wall of a pipe, for example, a large diameter pipe, for the purpose of reinforcement of the pipe so as to prolong its service life, it is desirable to apply a constant thickness of the coating material over a given length of the pipe. A spinner mounted to a sled that can be moved along the interior of the pipe to be reinforced provides an effective vehicle for spraying a coating material to the interior of the pipe. In order to actuate the sled, a chain may be secured to a leading end of the sled, and retrieval system may be provided to pull the chain, and thereby pull the sled, along the interior of the pipe. While the retrieval system could be in the form of a spool, it is recognized that during movement of the sled, as more and more of the chain is collected by the retrieval system and wound about the spool, assuming a constant angular velocity of the spool, the effective rate of movement of the sled decreases. As a result, unless the rate of spray of the coating material is adjusted, the thickness of coating material unacceptably increases as the sled approached the spool.